Abstract: Ventilation-windows were the main equipment for multi-span plastic greenhouse and its performance directly influencing the economic effect of greenhouse. The open, close, exact opening-angle of the ventilation windows was becoming increasingly important problems, because of the higher requirements of climate control in modern greenhouses. Adopting speediness, sureness, credibility, low cost pneumatics to design the operation of ventilation-windows was a reasonable solving method. The objective of the study was mainly to design a pneumatic operation system for ventilation-windows for multi-span plastic greenhouse. Mechanical effects were assessed, its cylinder load was calculated and a related model has been done. Compared the new self-developed system with the traditional gear-rack operation system for their mechanical characteristics, their operation, the control of windows opening, the windows-ventilation angle showed that the new system is more convenient, easy to use; easy to locate, the aperture angle is larger than that of the gear-rack operation system. The ventilation area was much increased and environmental conditions through ventilation were notably improved.